Test-circuit for multiple switch-boards



(No Model.)

0. E. S'ORIBNER. TEST CIRCUIT FOR MULTIPLE SWITCH BOARDS.

No. 467,902. Patented Jan. 26, 1892.

UNITED STATES CHARLES E. SCRIBNER,

PATENT OFFIcE.--

OF CHICAGO, ILLINOIS.

TEST-CIRCUIT FOR MULTIPLE SWITCH-BOARDS.

SPECIFICATION forming part of Letters Patent No. 467,902, dated January26, 1892.

Application filed May 29, 1891. Serial No, 394,500. (No model.)

To all whom it may concern:

3e it known that I, CHARLES E. SoRIBNER, a citizen of the United States,residing at Chicago, in the county of Cook and State of Illinois, haveinvented a certain new and useful Improvement in Test-Circuits forMultiple Switch-Boards, (Case No. 262,) of which the following is afull, clear, concise, and exact description, reference being had to theaccompanying drawings, forminga part of this specification.

Myinvention relates to a testing system for multiple switch-boards.

Its object is to provide means whereby an operator at one switch-boardmay ascertain whether any line is in use at some other board or not.

II eretofore many circuits or test systems desi ned to enable anoperator thus to determine whether a line called for was in use or nothave been devised; but under certain unfavorable conditions whichsometimes arise the sound or test-signal by which the condition of theline is indicated to a testing operator may be counterfeited by staticdischarges from a line, or by induced currents flowing in the linesescaping through the testcircuit to earth. Thus a false signal isproduced, which misleads the operator and causes confusion and delay inestablishing connection between subscribers.

My invention is designed to obviate this difficulty by providing atest-signal of such character as to be distinct and different from anysuch false signals.

My invention comprises circuits and apparatus whereby when a connectionis made to a telephone-line the branch circuit is completed to earth,including asource of intermittent or pulsatory electro-motive force ofsuch period and character that a current pro duced thereby is inaudiblein a telephone; means for testing the electrical condition of thetest-rings of a line, consisting of a testplug connected to earth by abranch circuit including a second source of intermittent or pulsatoryelectro-motive force of the same period and general character as thatfrom the first source, but whose periods of intermission coincide withthe periods of activity of the first source; a vibratingcircuit-breaker, and a telephone. Vhen a test-circuit including thesetwo sources of electricity is com pleted, as when a test-plug connectedto the second source is applied to the test-ring of a telephone-line towhich a branch circuit including the first source is attached, anundulatory current flows in the completed circuit, and is renderedaudible in the telephone by the action of the vibrating circuit-breaker,and produces in the telephone a fluctuating musical tone characteristicof the apparatus employed. A similar sound could not be produced in thetelephone by extraneous causes, since a static charge upon the linewould result in only a momentary hum in the telephone, while an inducedor foreign current would produce a continuous tone. hen an idle line istested, if the line be a metallic circuit no sound will be heard in thetestingtelephone. If it be a grounded circuit, an intermittent toneisproduced in the telephone, which is very distinct and difierent from thetone produced by the test of the line in use.

My invention will be more clearly understood by reference to theaccompanying drawings, which are illustrative thereof, in which- Figure1 represents three sub-stations connected by lines to their respectivespringjacks and annunciators upon two sections of multiple switch-board.The switch-board at the right of the drawings is shown equipped with thewellknown apparatus for connecting the different lines for calling andcommunicatingwith subscribers,and with myimproved testing system. Theswitch-board at the left of the drawings is shown equipped with thetesting system divested as far possible of its connections with thecalling-keys and their apparatus not concerned inits operation. Fig. 2is a graphical representation of the character of the electro-motiveforce impressed upon the circuit by one of the sources of currentincluded in the test-circuit. Fig. 3 is a similar representation of thecharacter of the electro-motive force of the other of the sources ofcurrent in the test-circuit. Fig. i is a representation of the compositecurrent resulting from the coaction of the two sources of current in thetest-circuit.

I will now proceed to describe in greater detail the system shown inFig. 1, and my inventioninconnectiontherewith. Sub-stations 1, 2, and 3are shown connected to their respective spring-jacks onthefirstandsecondsections of switch-board, l and 3 by metallic circuitsand 2 bya grounded circuit. Thecircuit from sub-station 1, for example,may be traced through line a,t-hroughline-spring and contact ofspring-jack a at the first section of switchboard, thence to theline-spring and contact of jack a at the second section of switchboard,thence through the annunciator a thence returning by line-wire a tostation 1. The line-spring and frame of answeringjack a are connected tolines a and a, respectively. The frames of jacks a and a are connectedto line d The line b from station 2 may likewise be traced through thelinespring and contact of spring-jack Z2, thence normally through theline-spring and contact of spring-jack b through the annunciator breturning by line I), resistance 1), and earth to station 2. Line 0 fromstation 3 extends likewise through spring-jacks c and 0 returning byline 0 The lines 0 c are not shown connected to their annunciator andanswering-jack.

The operating outfit at the second board comprises the two loop-plugs dand cl. The

tips of plugs d and d are electrically con-- them to the two sides of acalling-generator.

Branch connections are extended from the circuits joining the twoconnectingplugs d d tothe contacts of a listening-key 72, whereby upondepressing the key the telephone-set 2' is bridged in between the tipand sleeve of the plugs, and hence between the two sides of the circuitof two subscribers in communication. Asecond branch connection isextended from the wire joining the sleeves of the plugs (1 cl to thebrush k of a dynamo Z. The armature of dynamo Z I have shown as a singlecoil revolving in the magnetic field produced by the pole-pieces Z I.one is-connected to the segment 7c of a special commutator and the otherto the piece m.' This piece on is connected to earth through the brushm. Thesegment k is of such length as to engage with the brush 7c duringone halfrevolution of the armature. A second commutator-segment k isprovided in a position to engage with the brush during the rem aininghalf-revolution and is in electrical connection with the piece m.half-revolution of the armature the brush Zc receives current therefrom.During the other half-revolution the brush is is connected directly toearth through the segment 70 piece m, and brush m. Thus theelectro-motive force impressed upon the circuit of which brush 7c is aterminal will be of the character graphically shown in Fig. 2. As thearma- Of its two extremities Hence during one ture revolves theelectro-motive force rises from zero at n, the beginning of arevolution, to a maximum at 92 after one-fourth of a revolution, fallingagain to zero at n after half a revolution. During the secondhalf-revolution the brush 7c is upon the segment k and hence there is noelectro-motive force in the circuit. The period of fluctuation is suchthat separate pulsations of current through a telephone through whichthe circuit may be closed do not blend into a tone. I have found fifteenpulsations per second to be a suitable rate'of pulsation for thispurpose. The increase and decrease of the fluctuating current are sogradual as to be inaudible in a telephone, and the brush 7c is set atthe proper point to leave or to enter upon the segment 70 exactly at thepoints 17. 92 when the electromotive force is at zero. Hence no sound isheard in a telephone included in circuit with this dynamo.

In addition to the usual apparatus of an operators telephone set in myinvention I provide a connection from the middle of the coil oftelephone i, a branch connection extending to earth through a dynamo 0,similar to dynamo Z, already described, giving pulsations of the sameperiod and in the same direction as dynamo Z, but coinciding with theperiods of intermission of dynamo Z. The character of the current fromthis dynamo is represented in Fig. 3. Pulsatory currents having therelation to each other described that is, the pulsation of onecoinciding with the intermission of the other-I choose to designate ascomplementary currents. At the second boa-rd, at the right of thedrawings, I have represented this dynamo o by a circle. In connectionwith the testing outfit at the first board, however, it is representedascomplete. In shunt around that half of the telephone-coil which ismost directly connected to the tip of the test-plug, as d, I place avibrating circuit-breaker, preferably adapted to be actuated by thecurrent in .the branch circuit from the telephone to earth. This methodof connecting a circuit-breaker in shunt about a telephone-coil I havedescribed in an application for Letters Patent, filed February 24:,1891, Serial No. 382,358, wherein the peculiar advantages of this methodof producing a sonorous test-signal are set forth.

I will now proceed to describe the variousoperations involved inestablishingcommunication between two sub-stations by means of thesystem shown and to point outemore particularly the use of my testingsystem inconnection therewith. Suppose, for example, that the subscriberat station 1 desires to communicate with subscriber at station 3. Uponoperating his calling-generator the shutter of annunciator a is causedto fall. The operator at the second board inserts answering-plug d intothe answering-jack a of line 1 and depresses the listening-key h,whereby the lines a and a are extended through the contacts of thelistening-key to her telephone 2'. Hav- IIO ing ascertained the numberof the line with which subscriber at station 1 desires connection theoperator proceeds to test to determine whether lines from station 3 arealready in use at some other switch-board or not. This she does byapplying the tip of her testing-plug d to the test-ring of thespringjack of lines from station 3 at her board. The operation oftesting will be more readily followed by reference to the testing outfitat the first board. Here the testing-plug d is shown applied to thetest-ring of spring-jack b as in the act of testing the condition ofthat line. The lines from station 2 are notin use; but since the line D"is grounded a pulsatory current (represented in Fig. 3) will flow fromthe dynamo 0 through one-half the coil of telephone 93 and through thecoil and contacts of the vibrating circuit-breaker q, thence through thecontacts at one side of the listening-key? to the tip of the test-plug dthence through the line 17*, resistance b to earth, and returning todynamo 0. The vibrating circuitbreaker q will be at once thrown intovibration and an intermittent musical tone will be heard in thetelephone 29, which indicates to the operator that the line tested isnot in use. If the operator had tested a metallic circuitline which wasidle, no current would have flowed from dynamo 0, since the circuitwould. be nowhere closed to earth,and the silence in the telephone wouldsimilarly indicate the idleness of the line. Suppose, however, that theoperator applies the tip of the test-plug d to the test-ring of a linewhich is in use, as test-ring of jack a of line from station 1. Duringone-half of therevolution of the armature of dynamo 0 the current willflow, as before traced, to the test-ring of jack a, thence through. linea, through the sleeve of plug 01 to the brush 7.: of dynamo Z, thencethrough the segment k against which it bears at that instant, and brushm to earth. During the next half-revolution of the two dynamos, acurrent will flow from the armature of dynamo Z through the segment 7c,brush 7o, sleeve of plug cl, fragment of line a to test-ring of jack athence through tip of plug (1 one-half of telephone-coilp, and vibratingcircuit-breaker q, thence through the brush 3, segment 8 of dynamo 0,through the brush t to earth, and thence returning to dynamo Z. Thus apulsatory current made up of the alternate pulsations of current fromdynamos 0 and Z fiows in the testcircuit. The character of thiscomposite current is represented in Fig. 4. The

tone produced in telephone 19 will be of a correspondingly fluctuatingcharacter and will be very different and distinct from the tone producedby any accidentally-induced ourrent through the test-circuit, which mayexist occasionally.

It is obvious that the vibrating circuit breaker q might be includeddirectly in the earth branch from telephone 19; but I find thearrangement shown to be preferable.

Having thus fully described my invention, I claim as new and desire tosecure byLettcrs Patent 1. In a test-circuit for multiple switchboards,the combination of several electricallyconnected test -rings of springjacks, with a branch connection from one of the test-rings to earth,including a source of illtermittent or pulsatory electro-motive force,

a second branch connection from another of the test-rings to earth,including a telephone and a vibrating circuit-breaker in shunt thereof,and a second source of intermittent electro-motive force whosepulsations are complementary to and in the same direction in thetest-circuit as those from the first source, substantially in the mannerand for the purpose specified.

2. In combination with springjacks connected by telephone-lines with asub-station and furnished with test-rings electrically connectedtogether, a branch circuit extending from one of the test-rings througha source of intermittent or pulsatory electro-motive force to earth, andanother branch connection from another of the test-rings extendingthrough the coil of the telephone and through the contact points of avibrating circuit-breaker, and a second source of intermittentelectro-motive force whose pulsations are in the same direction relativeto the test-circuit as but coinplementary to the pulsations from thefirst source to earth, substantially in the manner and for the purposespecified.

3. In an electrical circuit, the combination of a source of intermittentelectro-motive force of constant direction relative to the electricalcircuit, a second source of intermittent elect-ro-motive force whosepulsations are complementary to and in the same direction in the circuitas those from the first source, a telephone, and a vibratingcircuit-breaker in shunt of the telephone, substantially as and for thepurpose specified.

In witness whereof I hereunto subscribe my name this 37th day of April,A. D. 1891.

CHARLES E. SGRIBNER.

XVitnesses:

ELLA EDLER, FRANK R. MOBERTY.

IIO

